The purpose of this grant request is to obtain an electron microscope and freeze-fracture replication instrument for the platelet research program of the co-investigators. This program is an orchestrated approach combining all ultrastructural investigative modalities with cytochemistry, biochemistry, immunochemistry and cellular physiology to problems of human platelet physiology and pathology in hemorrhagic disorders, thrombosis and host defense. A fully equipped transmission electron microscope of the finest quality has been and will continue to be the backbone of this research effort. For the past ten years this work has been conducted in a common-use electron microscopic facility of the Department of Pediatrics shared with several other workers in areas distinct from our hematological focus. Over recent years the requirements of the applicants and their research associates have expanded and become more critical while the quality of existing instrumentation has declined. Thus the effective and efficient conduct of this extensive research effort requires that we now obtain an electron microscope and freeze-fracture-etching unit for the exclusive use of our research team. The requested Philips EM 301 electron microscope and Balzer's Freeze-etch microtome will not only allow us to maintain our present level of productivity, but will expand our capabilities through special features of this equipment. The base of support for this research program comes from existing and pending grants of the NIH. This research will provide basic knowledge essential for understanding the relationships between structure and function in normal platelets and the defects in cell structure associated with abnormal physiology in human blood diseases.